using the histogram to determine exposure
Histograms display the relative levels of the darker to brighter tones. As the histogram stands, it isn’t of much direct use to us, since the tonality of the scene that was captured will dictate what the histogram shows us .. without a direct indication of whether exposure is correct.
Some will say that a histogram should have an even bell-shaped curve, but this is too simplistic. A light toned subject against a white wall will show a much different histogram that a dark toned subject against a dark wall .. even though the exposure might be correct in both instances.
In both those cases, the actual histogram display might be interesting to look at, but of no real direct use to us. But, here’s how I use the histogram to determine correct exposure …
For all that the histogram shows us, there is only one thing that is of direct consequence to us .. where the brightest relevant tone lies on the histogram. And I have to stress the word ‘relevant’.
It is no use looking at the histogram to determine exposure if there are bright patches of sky or highly reflective surfaces .. for this will skew the histogram display in making it appear like we are over-exposing, when it fact, we might very well have correct exposure.
With weddings (and portraits), the brightest relevant tone is most often the bride’s dress or groom’s shirt cuffs. So what I do is point the camera to an area that only contains the white dress / shirt, and no other bright areas. Then the most right-hand point on the histogram will be the white area. And then we can place that white tone correctly on the histogram .. and all the other tones will fall into place, whether skin tones or clothes or surroundings.
There is another way to approach this, and that is to spot-meter off only the relevant white area, and place it around 1.3 stops over the zero mark on your camera’s meter display. You don’t want to zero the meter reading then, since we don’t want the white to appear as grey. We want the white to appear as white .. and that will be around 1.3 stops to 1.7 stops over the zero mark. You will have to figure out the specific value for your specific camera, since there are some differences between the camera makes.
But back to using the histogram …
Here is what the Canon’s histogram will look like.
In my experience I have found I will get the best exposure if the brightest relevant area has the edge of the histogram appear half-way through the middle of the 5th block on the display, or 1/3rd from the edge of that display. It would seem that this varies a little between the various Canon D-SLR models, so it might be necessary for anyone who wants to use this method of calculating correct exposure, to interpet and apply this idea to the specific camera being used.
If I start over-exposing, then that kind of spike will start to appear.
With Canon D-SLRs (that I have experience of), the blinking highlights display won’t blink yet, but the image will appear too bright.
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The Nikon histogram looks slightly different:
In my experience, I get an optimally exposed image, if I have the edge of the histogram just barely not touching the corner of the histogram display … for the brightest relevant tone. (That term again. It’s an important distinction.)
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Here is the same image, but 2/3rd stop over-exposed. You can see the spike on the right-hand side. It looks different than the spike on the Canon histogram.
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From the above images, it should be obvious how I use the histogram to achieve correct exposure … I take a close-up view of the relevant brightest tone (some white area) .. and I place this at a very specific point on the histogram.
I lock this exposure value by using manual exposure mode, and all my images taken under the same lighting *will* be correct.
I’ve found this method to be consistent to the extent that I don’t use my flashmeter any more when using studio type strobes. (I use the Quantum flashguns.)
Andrea Lane Said,
August 4, 2007 @ 7:53 am
Thank you for this Neil. Very useful explanation.
Mearle Said,
August 7, 2007 @ 10:36 am
Neil, I can see clearly from the Nikon histogram where you have an over exposure, but your pair of examples with the Canon histogram seems strongly affected by the change in position of the bouquet of flowers that reduce the amount in the white wedding dress. Since the less white portion dress is covered, the remaining whites form a spike, not from overexposure, but but from a reduction of white data. I would contend that you still have a properly exposed image on the Canon at 1/100 f5.0, especially if you are shooting in RAW instead of JPEG.
Neil Said,
August 8, 2007 @ 3:54 pm
Rodolfo Rodriguez Said,
October 6, 2007 @ 3:54 pm
Dear Neil:
Congratulations for your blog. 10 over 10 !
With your familly name sure you are from NL or the north of BE.
Aren’t you ?
Smart people from those lovely countries have a very special quality teaching confuse things into untestardable ones. No matter which topic.
I am proud to tell you that I lived and work during 3 years in Antwerpen, (Berchem) 35 years ago working by Agfa-Gevaert in Mortsel.
Where my main photographic and electronic backgound comes from. Please keep in touch
Rodolfo, from Argentina
Kafka Said,
January 7, 2008 @ 9:15 am
Hi,
Thanks again, Neil.
I was doing similar things with manual metering mode or by adjusting exposure compensation with aperture priority mode, but your techniques gave me for the first time a clear and practical principle which saved me from my fuzzy method.
I am curious now. If I may describe your technique as a “high key” metering, do you use a “low key” metering technique, if there is, when you want black to appear as black as far as possible? How would you adjust by looking at the histogram or that’ll always require us to dial the exposure compensation as per experience?
Kafka
Desmond Said,
January 10, 2008 @ 3:23 am
Hi Neil , I am also from SA , living in New Zealand now . I want to take control of exposure by going manual and this has been a very useful instruction for me .
Cheers , Desmond .
George Said,
January 16, 2008 @ 4:59 pm
Hi Neil,
Great site, and I like this technique. I see how it can be very useful in controlled settings such as the studio. But, how do you manipulate this fast enough to keep up with the fast pace and ever changing lighting of weddings, especially outdoors? Is there a different technique you use for that? If so, please share.
Thank you,
George
Ross Said,
February 19, 2008 @ 10:03 am
Hi Neil,
Great tutorial, helps me a lot with achieving the correct exposure. However I too would be interested in how you use this technique in Candid shots when you are moving around frequently.
Ross
Neil Said,
May 15, 2008 @ 11:04 pm